A new breast cancer treatment could change how doctors detect and respond to treatment resistance.
The US Food and Drug Administration (FDA) has approved camizestrant, marketed as Etcamah, for certain patients with hormone receptor-positive (HR-positive), HER2-negative advanced or metastatic breast cancer. What makes the approval significant is that treatment can be guided by a blood test detecting a genetic resistance mutation before scans show cancer progression.
Camizestrant is designed for patients whose tumours develop an ESR1 mutation while they are receiving hormone therapy along with a CDK4/6 inhibitor.
ESR1 mutations can make breast cancer resistant to aromatase inhibitors, a commonly used form of hormone therapy. Detecting the mutation in circulating tumour DNA, or ctDNA, can provide an early signal that the cancer may be developing resistance to the existing treatment.
Instead of waiting for a scan to show that the disease has progressed, doctors can use the blood-test result to consider changing treatment earlier.
The FDA described the approval as the first cancer therapy approved based on detecting a resistance mutation in circulating tumour DNA before imaging shows disease progression.
Camizestrant is an oral drug belonging to a class called selective estrogen receptor degraders (SERDs).
It targets estrogen receptors and helps prevent estrogen from stimulating hormone-sensitive cancer cells. The FDA approval allows camizestrant to be used alongside one of three CDK4/6 inhibitors: abemaciclib, palbociclib or ribociclib.
The companion Guardant360 CDx blood test was also approved to identify patients with ESR1 mutations who may be eligible for the treatment.
The approval was supported by the Phase III SERENA-6 trial, which included 315 adults with HR-positive, HER2-negative locally advanced or metastatic breast cancer.
Patients who switched to camizestrant after an ESR1 mutation was detected had a median progression-free survival of 16 months, compared with 9.2 months among those who continued their previous aromatase inhibitor-based treatment.
However, there is an important caveat: overall survival data were not yet mature when the FDA evaluated the trial's primary outcome.
ESR1 mutations are relatively uncommon when HR-positive metastatic breast cancer is first diagnosed but can become more common after treatment with aromatase inhibitors.
According to the FDA information cited by NDTV, fewer than 5% of patients have the mutation at initial diagnosis, while nearly 40% may develop it after disease progression on an aromatase inhibitor.
That makes monitoring the mutation potentially valuable: the cancer's genetic behaviour can change even while scans still show no obvious progression.
Camizestrant received accelerated FDA approval, which means additional studies are required to confirm its clinical benefit. Continued approval can depend on the results of those confirmatory studies.
The significance of the development therefore isn't that a blood test can replace scans altogether. Rather, it marks a shift toward using molecular signals in the blood to detect treatment resistance earlier and potentially change therapy before conventional imaging shows progression.
For patients with eligible advanced breast cancer, that could mean getting a new treatment strategy at a point when the disease has not yet become visibly worse on a scan.
